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Old 17 April 2014, 08:26   #1
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Cheap SIB for 6hp Longshaft

I wouldn't mind a cheap SIB that I could use with a 6hp Mariner 4 stroke I already own which is the aux on my Raider 18. Anyone any thoughts or am I wasting my time and I should just buy a short shaft as well? I was thinking about using it in the Dee or further inshore in the Mersey for a bit of playing about and maybe a little bit of fishing.
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Old 17 April 2014, 08:42   #2
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As you have guessed, all small sibs use shortshaft outboards. A couple of the larger and newer Zodiac Futura's use long shafts, but they wouldnt be much fun with a 6hp motor.

Long shafts are not ideal on shortshaft transoms, the 2 biggest issues are stability and drag when on the plane and also occasionally too much back pressure on the exhaust resulting in poor starting. About 20 years ago I did use the long shaft auxillary from my hardboat on a Zodiac C240 slat floor tender. The boat wouldnt plane, but with a 2" shim on the transom it ran fine at displacement speeds with no stability issues.

FWIW I would give it a go, worst case you have to sell the sib for a few quid loss.
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Old 17 April 2014, 08:55   #3
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Thanks for that, that was pretty much what I thought, the drag would be significant with such a low powered boat too I think.
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Old 18 April 2014, 10:00   #4
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You can use a long shaft on a short transom and perform well. Some isssues, will depend on boat size if easy to plane as opposed to a shorter one which has more hull drag to overcome fast from a dead stop with a non ideal HP engine.

Will have water splashess at back transom which can de solved by installing a second water deflector plate on lower unit, will need to find it by yourself with a wot water test.

Do you have already the sib or you are planning buying one shortly and would need an advice about its size ? Depending on the size could achieve from fast displacement to plane speeds..

Happy Boating
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Old 18 April 2014, 10:41   #5
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Cheers. I was looking for something just for fun in calmish water. I already have a fast fisher type of boat but would have liked something to play on and maybe fish some of the shallower bits of the mersey and the dee. It would only ever be two persons max and I want a sib as I already pay enough marina fees lol. So I already have a long shaft four stroke 6 that weighs 25kg and would have liked to use that if possible. I'll listen to any and all advice
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Old 18 April 2014, 20:36   #6
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Would a 320 Mt sib suit you ? If larger will be faster to plane. The drag using a long shaft on a short shaft transom is minimum, bear in mind that lower tails are round or have a sharp edge wich cuts water flow much friendly than if being a square one, that definitely will have more drag when trying to plane from a dead stop along unwated water splashes over/out transom.

On the market you can find sibs with long transoms, don't know about UK though.

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Old 19 April 2014, 04:13   #7
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Deffo reccomend a sib greater than 3.2 as these can take up to a 15hp but these are heavier
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Old 19 April 2014, 04:33   #8
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There are a couple around near me I might have a look at like;

http://www.preloved.co.uk/adverts/sh...nflatable.html

And;

http://www.preloved.co.uk/adverts/sh...-outboard.html

Having said that I should just go boating about while the weather is nice lol
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